1. Field of the Invention
The invention relates to polymeric viscosity index (V.I.) improver - dispersant additives for lubricating oils. This invention also relates to processes for preparing grafted and amine functionalized olefin polymers and their use in oil compositions, and includes an improved solution process for grafting unsaturated moieties, e.g. maleic anhydride, vinyl monomers, etc. onto the olefin polymer by carrying out the graft reaction in a solution medium comprising certain polymeric hydrocarbon diluents.
2. Prior Disclosures
Olefin or hydrocarbon high molecular weight polymers such as hydrogenated copolymers of isoprene and butadiene, copolymers of butadiene and styrene, and ethylene copolymers, particularly ethylene-propylene copolymers are known as viscosity index (V.I.) improving additives for oil compositions, particularly lubricating oil compositions. A substanial body of prior art exists directed towards further reacting these ethylene V.I. improvers to form a multi-functional V.I. improver. This is a material useful as a V.I. -dispersant oil additive so as to improve not only the V.I. properties of the oil but to also impart dispersancy so as to suspend sludge that may form during the operation or use of the lubricant and to inhibit varnish deposition in engines. Examples of such prior art include patents which teach grafting ethylene copolymers with maleic anhydride, followed by reaction with an amine, such as U.S. Pat. Nos. 4,137,185, 4,144,181 and 4,089,794. Similarly, prior patents, such as U.S. Pat. Nos. 4,092,255, 4,146,489 and 4,170,561, were directed towards grafting the ethylene copolymer directly with a nitrogen compound such as vinyl pyridines and vinyl pyrrolidones.
The early patents such as U.S. Pat. Nos. 3,316,177 and 3,326,804 taught the general concept of grafting an olefin polymer, e.g. ethylene-propylene copolymer, with maleic anhydride and then reacting with a polyalkylene polyamine such as polyethylene amines. Subsequently, U.S. Pat. No. 4,089,794 was directed to using an oil solution for free radical peroxide grafting the ethylene copolymer with maleic anhydride and then reacting with the polyamine. This concept had the advantage that by using oil, the entire reaction could be carried out in an oil solution to form an oil concentrate, which is the commercial form in which such additives are sold. This was an advantage over using a volatile solvent for the graft reaction, which has to be subsequently removed and replaced by oil to form a concentrate.
U.S. Pat. Nos. 4,036,766 and 4,036,767 disclose improved polymeric additives from acrylic and methacrylic acids, useful in lubricating oil and ATF to impart desirable viscosity temperature characteristics, prepared by polymerizing the acrylic monomer components in the presence of a polyalkene-1. These references indicate that the polyalkene solvent may form a complex with or otherwise associates with the polymethacrylate to increase the solubility of the polymethacrylate in the oil. U.S. Pat. No. 4,036,768 contains a similar disclosure in the preparation of these interpolymers having the same viscosity advantages except that the polymerization is carried out in the presence of a liquid polyalkyl benzene which is believed to provide improvements in dispersancy and oxidative stability by the same polymer solvent association or complexing.